Fickle Sentries

Some logic puzzles inspired by those of Raymond Smullyan.

Based on the text below, make your selection by clicking next to the
treasure type you expect to find in the cave. Click the Solve
button to confirm your selection. If you are stumped, use the Reveal Explanation
button (once this is clicked, you can no longer submit a solution).

Two guards are standing outside the entrance to a cave, guarding the treasure within. The treasure is one of copper, silver, gold, platinum, diamonds, or rubies.

Guard 1 lies when guarding copper, silver, or gold and tells the truth when guarding other treasure. Guard 2, on the other hand, lies when guarding platinum, diamonds, or rubies, but tells the truth when guarding other treasure.

In this land, copper is worth less than silver, which is worth less than gold, which is worth less than platinum, which is worth less than diamonds, which is worth less than rubies.

You meet the guards at the entrance to the treasure cave, and they make these statements:

If you determine the contents of the cave, the guards will let you pass and you can claim the treasure.